New answers tagged conservation-laws
-1
votes
Why is $\mu\to e \gamma$ forbidden in the SM w/o neutrino masses?
a) Densidade Lagrangiana para Elétrons e Múons Acoplados ao Eletromagnetismo
A densidade Lagrangiana para elétrons acoplados ao eletromagnetismo é dada por:
𝐿
−
1
4
𝐹
𝜇
𝜈
𝐹
𝜇
𝜈
+
𝜓
ˉ
(
𝑖
𝛾
𝜇...
1
vote
Motion of fragments
If we assume that all the fragments have the energy, then for three fragments, we have that the momentum vectors have equal lengths, and their sum is zero. The sum of vectors is geometrically ...
- 9,116
0
votes
Particle A decays to particle B and massless particle C
You indeed do not have enough information to solve for the mass of B.
A helpful physicist’s trick is to always look at the most extreme cases, for instance, “I know this is some sort of rotation so ...
- 39k
3
votes
Motion of fragments
is it even possible to accurately predict the motion of the fragments of an ideal body given that it splits into equal masses?
No, at least, not if all we are given is that the system conserves ...
- 109k
1
vote
Motion of fragments
In a nutshell, is it even possible to accurately predict the motion of
the fragments of an ideal body given that it splits into equal masses?
Why wouldn't it?
For conservation of momentum, if the ...
- 77.9k
0
votes
Motion of fragments
Yes, it is possible to predict the movement of fragments that break apart in parts of equal mass. Consider that the energy must be evenly divided among the bodies, which results in all bodies having ...
8
votes
Accepted
Motion of fragments
In general, you would need very precise, and often unattainable, information about the internal structure of the fragmented body, the exact nature of the stresses that caused it to fracture, and a ...
- 3,397
1
vote
Condition on conserved quantities to escape Kerr black hole
Consider a test particle of mass $m$ moving in the Kerr spacetime, described by the metric in Boyer-Lindquist coordinates $(t, r, \theta, \phi)$:
$$ ds^2 = -\left(1 - \frac{2Mr}{\Sigma}\right)dt^2 - \...
- 764
1
vote
Is flavor a charge? Is there a field associated with flavor?
No, flavour is not a charge. In physics, the word charge is usually saved for the conserved quantities under group symmetries. Thus electric and colour charges are fundamental in the Standard Model ...
- 332
1
vote
Is flavor a charge? Is there a field associated with flavor?
Color is an observation that does not translate very well to classical physics.
There's no "part" of a hadron that has any particular color more than another color, it's not like poles of ...
- 29
1
vote
Does fixing particle number + only evolving to lower energy states make the simulated system isolated?
If a system is completely isolated, then it will neither gain nor lose energy, i.e., its energy is fixed. A system whose energy is exactly specified will take on states drawn from the microcanonical ...
- 51.6k
2
votes
Accepted
What is the Carter constant?
In very basic terms, the Carter constant is a mathematical quantity that helps about the description and predictability of particle’s motion around a rotating black hole.
There are four quantities ...
- 355
3
votes
What is the Carter constant?
The square root of the Carter constant has the units of angular momentum. In Schwarzschild it reduces to the covariant angular momentum in the θ direction, while in Kerr it corrects for the frame ...
- 13k
0
votes
Is conservation of momentum and energy valid for non-inertial frames?
Balance of momentum and energy (and also angular momentum) is valid in any frame and any coordinate system. It's important here to make a distinction between a balance law and a conservation law.
For ...
- 3,833
0
votes
Why does a smaller mass gain higher speed in an elastic collision with a larger mass?
Think of the large mass as a great big moving wall. Now imagine sitting on the wall. As far as you are concerned, the wall stays still while some small thing (a ping-pong ball or whatever) comes along ...
- 61.8k
2
votes
Why does a smaller mass gain higher speed in an elastic collision with a larger mass?
Because of Newton's Third Law, the masses experience the same magnitude force during the collision. The smaller mass will experience a larger acceleration due to Newton's Second Law. So, in most ...
- 24.7k
1
vote
Accepted
Why does a smaller mass gain higher speed in an elastic collision with a larger mass?
The first thing to do is work in the center-of-mass frame ($F$), where:
$$ p_i = -P_i $$
which scatters to:
$$ p_f = -p_i $$
$$ P_f = -P_f $$
(note: this is a 1D problem, so I am not using vector ...
- 39.5k
2
votes
Why is rotational kinetic energy not explicitly considered in the energy analysis of a simple pendulum?
The simple pendulum is idealized. The bob is treated as a point mass. Furthermore, the amplitude is kept small enough that $sin(\theta) \approx \theta$. The mass of the rod is ignored. Friction is ...
- 45.7k
0
votes
Difference between weak and strong interactions?
You can check which interaction is going on by checking whether $I_3$ (isospin) is conserved or not. If not, then weak interaction is present. Otherwise, it is strong/electromagnetic interaction.
6
votes
Accepted
Under what conditions will a circuit violate conservation of charge and/or conservation of energy?
Kirchoff’s current law (KCL) implements the conservation of charge in a circuit. Kirchoff’s voltage law (KVL) implements the conservation of energy in a circuit. See Boundless Physics, various online ...
- 109k
4
votes
Why do some nuclei decay exclusively via positron emission rather than electron capture?
You are correct that electron capture is always possible for any isotope that can decay by positron emission. The reverse is not true. It can be confusing that electron capture and positron emission ...
- 13.2k
3
votes
Beta decay of 6-Helium
Hans Bethe and Philip Morrison give the following "hand-waving" answer to this question on pages 226-227 of the 2nd edition of their influential non-textbook on nuclear physics titled ...
5
votes
Why do some nuclei decay exclusively via positron emission rather than electron capture?
While summaries on various websites can provide a high level overview, if you want real details one should go to something like the Evaluated Nuclear Structure Data File (various mirrors around the ...
- 7,876
Top 50 recent answers are included